Electric heating furnace



1961 H. J. FERGUSON 2,971,076

ELECTRIC {HEATING FURNACE Filed July 20, 1959 2 Sheds-Sheet 1 ATTORNEY.

Feb- 7, 19 H. J. FERGUSON ECTRIC HEATING FURNACE 2 Sheets-Sheet 2 FiledJuly 20, 1959 FIGURE 4 FIGURE 5 FIGURE 8 FIGURE 7 FIGURE 6 ELECTRICHEATING FURNACE Henry J. Ferguson, Kalispell, Mont. (800 N. 23rd St.,Coeur dAlene, Idaho) Filed July 20, 1959, Ser. No. 828,314

4 Claims. (Cl. 219-39) This invention relates generally to an electricair heating and conditioning system, for a relatively small space, inwhich air is recirculated through said space by means of anappropriateduct work.

' More specifically the invention relates to an electric furnace and aircirculating device for trailers or mobile homes designed especially forits small size, high efficiency, simple installation and ease inoperation.

The principal object of the invention is to provide a new and novelelectrical furnace of a small compact nature and of economicalconstruction that may be readily used to heat a house trailer.

A further object of my invention is to provide a device as aforesaidthat may also, during the summer months, be used to circulate filteredair through a house trailer.

A further object of my invention is to provide a device as aforesaidthat is simple to install and does not require professional orspecialized services of a furnace installer or an electrician in theinstalling process.

A further object of my invention is to provide such a device that hassafety features to prevent the electric heatlug-element from becomingoverheated and one that does not create too great an initial surge incommencing operation.

A still further object of my invention is to provide a new and novelcombination of electrical heating element with a thermostat to give agreater temperature stability within a furnace and prevent the excessiveswitching on and off of the device.

While the foregoing objects are paramount, other and lesser objects ofmy invention will be set forth and become readily understandable fromthe preferred embodiment thereof set forth in this specification.

' The specification is to be construed and interpreted in relation withthe accompanying drawings which illustrate the specific embodiment, andwherein like numbers of reference refer to similar parts throughout allfigures, and in-which:

Figure 1 is a front vertical surface view of the entire furnace cabinet.

Figure 2 is a vertical cross-sectional view of the furnace cabinet withthe door removed, thus showing the filter and furnace proper, taken onthe line 2-2 of Figure 1 in the direction indicated by the arrowsthereon.

Figure 3 is a vertical cross-sectional view of Figure 1, showing theinternal structure of the furnace, taken on the line 33 of Figure 1 inthe direction indicated by the arrows thereon.

Figure 4'is an electrical circuit diagram showing, diagrammatically, theelectrical circuitry of my invention.

Figure 5 is an isometric view of the thermostat used in my furnace,showing its shape and the manner of limiting its motion.

Figure 6 is an isometric view of the preferred bar form of heatingelement of my furnace.

Figure7 is a vertical. cross-sectional view of Figure 6 taken on'theline 7--7 in the direction indicated by the arrows thereon.

Figure 8 is an isometric view of a coil-type heating element that may beused in place of the bar elements in the preferred form of heating unitof my invention.

Referring now to the drawings, and particularly Figure 1, it will beseen that my furnace is completely contained within a relatively smallcabinet 11. This cabinet 11 is divided into an upper smaller chamber 12and a lower or furnace chamber 13 by the filter 14. The filter 14 is ofthe ordinary variety of commerce slidably supported Within the furnacecabinet 11 by the channels 15, mounted thereon. Air is permitted freepassage into the upper filter chamber 12 through the screen 16 in frontof the upper chamber 12 of the furnace cabinet 11.

The lower furnace chamber 13 is of such appropriate size as to containthe blower assembly 17 and the furnace bonnet 18. The blower assembly 17comprises a housing 50 shaped substantially as illustrated in Figure 2,communicating with the uppermost portion of the furnace bonnet 18 andcontaining a squirrel-cage type fan 19 actuated by the internallycontained electric motor 20, preferably, but obviously not necessarily,of the shadedpole type. This fan assembly 19, well known in the art,takes air from the furnace chamber 13 through the central orifice 21 andpropels it with downward velocity into the interior of the furnacebonnet 18. l

The furnace bonnet 18 is a rectangular structure shaped substantially asillustrated, preferably constructed from sheet metal, because of itsease in handling and fabrication.

The blower assembly 17 communicates with the in-" terior of the furnacebonnet 18 through the orifice 22 in the top of the said bonnet 18. Theheating element 23 is supported within the furnace bonnet 18 in acentral posi: tion spaced from the walls of the bonnet 18, by brackets24 supported on the walls of the bonnet 18. I prefer to releasablyfasten the flanges 51 of the heating element 23 to the brackets 24 withbolts or metal screws (not shown) so that the element may be readilyremoved should the occasion demand. The heating element 23 must bespaced away from the walls of the bonnet 18 to prevent the walls frombecoming overheated, but yet must be such as to require a substantialportion of the air passing through said bonnet to pass over or near theheating bars 33, 34.

An air duct 25 communicates with the chamber of the furnace bonnet 18and thence outwardly through the front of the furnace cabinet 11 to thegrill 26, which is provided with the damper 27 to regulate the air flowtherethrough. This duct 25 may be opened to provide a quick heating nearits orifice.

The bottom portion of the bonnet 18 is provided with the outwardlyflared flange 28 and the sheet 29, preferably of asbestos material, bothof Which provide means of fastening the furnace bonnet to an appropriatesupport and connecting it to an appropriate duct system (not shown). Iprefer to releasably fasten the flared flange 28 to its floor supportwith wood screws or the like so that it can be readily placed andremoved at will. An orifice 30 may be easily provided in the asbestossheet 29 with such appropriate size and positioning as will providemeans of communication with an air duct 31 which communicates in turn tothe various parts of the space to be heated.

A preferred form of heating element for my furnace is illustrated inFigure 6 of the accompanying drawings. This heating element comprisesthe outer flanged box 32, having bar-type resistance heating elements 33spaced perpendicular to two of the sides of the box 32 in the upperportion thereof and having similar bar type resistance heating elements34 in the lower portion thereof spaced perpendicular to the direction ofthe elements 33; A thermal cut-out switch 35 is provided on the box 32to prevent an overheating thereof. I prefer to use a bar-type PatentedFeb. 7, 1961 I aa'rrm'e resistance heating element 33, 34 asillustrated, because of the slower more even heat of lower temperatureand the-greater heating surface offered byrthistype of element, butother types of elements mayserve well and may have other advantages.Another type of element that has been found to beeifective is that shownin Figure 8, comprising a' porcelain matrix 36 carrying the spiralwire-wound resistance element 37. This type element may be affixed inthe upper and lower positions of the box 32 bybolting at the appropriateposition. This type element 37 has the advantage of providing a fasterheat but the disadvantage of a much more rapid heat loss and smallerheat transfer Surface.

The internal heat responsive switching. device or thermostat 38 is bestillustrated in Figure 5. The switch proper is contained inthe box 39,but the heat sensitive portion of the thermostat comprises a relativelyelongate, cylindrical member 40, and this shape is somewhat critical.The thermostat 33 must be positioned in and on the heating element 23 sothat the heat sensitive member 43 is between the upper heating. element33 and the lower heating element 34 and extends a substantial distancebetween the said heating elements 33, 34. Thermostats having such aconstruction are well known in the art. Many of such thermostats arecontinuously variable in their make-break point and for safety reasonsit often becomes convenient or even necessary to limit this makebreak'point, particularly as to the highest temperature. Such devices normallyhave a diai-type indicator 41, as illustrated, and I have found in usingthis type indicator that a convenient maximum stop may be established inthe device merely. by appropriately positioning a screw 42 in the casingto prevent the temperature selecting device 41 from passing beyond acertain predetermined safety point. a. continuously variable type, asone with only high and low make-break points will ordinarily serveequally well.

The. electrical circuitry of my device is illustrated, diagrammaticallyin Figure 4 of the accompanying drawings. I prefer to operate the systemon ordinary commercially available alternating 220 volt split two-phasecurrent. The current is manually controllable by the on-, off switch 52,and is transmitted, in'series, to the external line-voltage thermostat45, appropriately located at some point in the area to be heated. The220 volt current is thence supplied, in series, to the lower bank ofresistance heating elements 34. Thus when the thermostat 45 is closedand calls for beat, this circuit is completed and the lower heaterelements 34 begin supplying heat.

Because of the relatively great current required to operateall of theheating elements 33, 34, it is desirable and often necessary to dividethe upper 33 and lower 34 heating elements into two separatelycontrolled circuits, the upper to become operative after the lower, toprevent too great an initial surge of current across the supply lineswhen the device actuates. This second circuit for the upper bank ofheaters 33 is in parallel with the first on the controlled side of thethermostat 33, and is closed or activated by the switching-relay 44.

This switching relay 44, preferably adapted to operate at 110 volts, isactivated to a closed position by the thermostat 38 between the heatingelements 33, 34 and when this thermostat 38 closes it also completes the110 volt circuit through the variable rheostat 4-9 in series with thefan motor 20.

A manual-reset safety thermostat 35 is provided in series with bothheater circuits to cut out the circuits should the heaters 33, 34 orbonnet 1% become overheated by reason of fan failure or other cause.

In operation, when the external thermostat 45 calls for heat, current isallowed to pass into the lower bank of resistance heating elements 34which begin the heating Y h n h sslqwer nk 4 a ses he. m e a r of-thethermostat 38 to a predetermined point, both the It is not necessarythat this thermostat 30 be offan and relay circuits are activated. Therelay-44 closesand thus supplies current to the second or upper bank ofheating elements 33. Current is also supplied to the fan motor whichbegins its operation to cause the fan 19 to force air over the heatingelements 33, 34. The speed of the fan may be varied by regulation of thevariable rheostat 49.

When suflicient heatis supplied to thethermostat 45 and it opens, theheater elements 33, 34 are immediately cut out, but-the fan circuitand-relay cireuitremain closed and the fan 19 continues to operate untilthe thermostat 38 between the heaters 33,34 cools sufiiciently to openits circuit.

The thermostat 38 between the heaters is adjustable, so that its uppercut-in and lower cut-out point may be varied; it may be continuouslyvariable between limits or variable only between two limits. I-prefer tohave the thermostats upper limit. at approximatelyv degrees Fahrenheitas hereinafter described to prevent-the bonnet 18 and its parts fromoverheating, Thelower, cut-in point should be at approximatelySO'degrees Fahrenheit or below, for my invention to be adapted tosummer-circulation. i

If it should be desired to usethe-fan for air conditioning orcirculation without heat, as. well'it might in the summertime, the.cut-in point of the thermostat 38 i set at is lowest limit, which wouldbe below the existing room temperature, and the fan circuit is thenactivated without activation of the heating elements 33,34. To stop thefan the thermostat 38is turned back t9 its highest cut-in point and thecircuit'is broken as this temperature is well below the roomtemperature,

It should be noted that therheostat 4,9 has nooff-posi-v tion forsafetyreasons. If the heaterelement becomes sufficiently hot the fanmust be activated, and-thus prevent a possible overheating.

The air flow through the devicewhen it is operating-is readily apparentfrom the drawings. Air is taken in through the orifice 21 in the blowerassembly 17, thus creating an air flow from the outside through thescreen 16 into the filter chamber 12, thence through the filter-15 andinto the furnace chamber 13 from whence theair circles through theheating elements, the blower assembly and over out into the duct system(not shown). and back into the room to eventually follow the samecircuit again.

Although the foregoing description is necessarily of a detailed specificcharacter in order that a specific embodiment of my invention may becompletely set forth, it is to be understood that thisspecificterminology and:structure is not intended to be restrictive orconfining, and that various rearrangements of'partsand modfficationofdef tail may be resorted to without departing fromv essence, scope orspirit of the invnetion herein disclosed and'hereinafter claimed.

Having thusly described my invention, what I desireto protect by LettersPatent and what I claim is:

1. In an electric air heating and circulating device of he natureaforesaid, a cabinet having a smaller. filter chamber providingrelatively free air passage thereinto, communicating through a filterwith a relatively larger furnace chamber havinga furnace thereincomprising in combination, an elongate bonnet; a variable means ofcausing air flow downward therethrough; a heating element positionedtherein, in spaced relation with the walls of said bonnet, having aplurality of bar-like electrical resistance heating elements arranged inan upper bank and a lower bank with the elements of each bank mutuallyparalleled to each other and perpendicular to the elements of the otherbank; an external thermostatpositioned in the areato be heated, adaptedto allow current to besupplied to thelower bank of said resistanceheating,

elongate temperature sensing member positioned between said upper bankand said lower bank of resistance heating elements, adapted to permitcurrent to be supplied to the upper bank of said resistance heatingelements and to actuate said means of causing air flow through saidbonnet when said internal thermostat is heated to a predeterminedtemperature; a manually resettable safety thermostat adapted tointerrupt the flow of current to said heating elements at a certainperdetermined safe operating temperature; means of supplying electriccurrent to said circuits; and means of conducting heated air from saidbonnet.

2. In an electric air heating and circulating device of the natureaforesaid, in combination, a rectangular bonnet; a blower mountedthereon and communicating therewith adapted to cause a variable air flowdownward through said bonnet; a heating element positioned therein inspaced relation therewith, having an upper heating member and a lowerheating member in spaced relation with each other, each of said heatingmembers being adapted to permit the relatively free passage of airtherethrough; a variable external thermostat positioned in an area to beheated and adapted to allow current to be supplied to one of saidheating members when the temperature of said external thermostat fallsbelow a certain predetermined point; a variable internal thermostat,having a relatively elongate temperature sensing member positionedbetween said upper heating member and said lower heating member, adaptedto cause current to be supplied to said other unheated, heating memberand to actuate said blower to cause air flow through said bonnet whensaid internal thermostat is heated to a predetermined temperature; a'manually resettable safety thermostat adapted to interrupt the currentflow to said heating elements at a predetermined safe operatingtemperature; means of supplying electric current to said circuits; andmeans of conducting heated air from said bonnet.

3. In an electric air heating and circulating device of the natureaforesaid, the combination of a heating element having a plurality ofbar-like electrical resistance heating elements arranged in an uppergroup of mutually parallel elements all perpendicular to a lower groupof mutually parallel elements in spaced relation therewith;

an internal thermostat having a relatively elongate temperature sensingmember positioned between said upper group and said lower group ofheating elements, said thermostat being adapted to allow electriccurrent to be supplied to one of said groups of the heating elementswhen heated to a predetermined temperature by the other of said groupsof heating elements; and means of supplying electric current thereto.

4. In an electric air heating and circulating device of the natureaforesaid, the combination of a lower heating element controlled by avariable external thermostat in series therewith, adapted to allowcurrent to be supplied thereto when the temperature of said externalthermostat falls below a predetermined point; an upper heating elementin spaced relation therewith, electrically connected in parallel withsaid lower heating element and in series with said external thermostat,controlled by a variable internal thermostat, in series therewith, saidinternal thermostat having a relatively elongate temperature sensingmember positioned between said upper heating element and said lowerheating element and being adapted to activate a relay causing current toflow in said upper heating member when said internal thermostat isheated to a predetermined temperature; a fan in series with saidvariable internal thermostat and with a variable rheostat adapted toregulate the speed of said fan, said fan being energized when saidinternal thermostat is heated to a predetermined temperature; a manuallyresettable safety thermostat in series with both of said heatingelements adapted to interrupt the current thereto if heated to apredetermined unsafe operating temperature; and means of supplyingelectric current to said circuits.

References Cited in the file of this patent UNITED STATES PATENTS2,061,258 Soverhill Nov. 17, 1936 2,471,784 Seifner et a1 May 31, 19492,544,544 Qualley et al. Mar. 6, 1951 2,697,164 Knapp et al Dec. 14,1954 FOREIGN PATENTS 579,133 France July 24, 1924

